Method and apparatus for sound insulation



R. A. FESSENDEN.

METHOD AND APPARATUS FOR SOUND INSULATION.

APPLICATION FILED FEB. I, 1919.

1,348,828. aten ed Ailg. 3, 1920.

Inventor By Attorneyr fink My UNITED STATES PATENT OFFICE REGINALD A. FESSENDEN, OF BROOKLINE, MASSACHUSETTS, ASSIGNOR TO SUBMA- RINE SIGNAL COMPANY, OF PORTLAND, MAINE, A CORPORATION OF MAINE.

METHOD AND APPARATUS FOR SOUND INSULATION.

Specification of Letters Patent.

Application filed February 1, 1919. Serial No. 274,562.

To all whom. it 'nmg concern:

Be it known that l, REGINALD A. F nssnN- mm, of lirookline, in the county of Norfolk and State. of Massachusetts, a citizen of the United States, have invented certain new and useful Improvements in Methods and )paratus for Sound Insulation, of which the following is the specification.

My invention relates to the propagation in liquids of compressional waves, such as sound waves and explosive. waves, and has for its object the prevention and suppression, and shielding from the effects of, such waves.

Figures 1 and 2 show, partly diagrammatically, apparatus suitable for carrying out my invention.

Heretofore in operations concerned with the propagation of compressional impulses such as sound waves and explosive waves, difficulty has been met with in attempting to prevent the propagation of such waves, and in attempting to screen objects from them. Many arrangements have been devised to accomplish these results, but the methods and apparatus herein described possess certain advantages and in certain important cases afford the only means of accomplishing these results.

Applicant was led up to the invention herein described by discovering, while experimenting with his oscillator (U. S. Patent 1,167,366, issued January 4, 1916), that the inflated inner tube of an automobile tire, on being placed in proximity to the oscillator, prevented it from generating compressional waves or from receiving them. Further experiments developed the fact that bubbles in the liquid vhether allowed to issue freely from an air pipe, or retained in a thin flexible tube, such as the inner tire tube above referred to, were extremely efficacious in preventing the propagation of compressional waves and in shielding objects from effects of such waves. Applicant thereupon devised various types of screens and shields for sound waves and explosive waves, and filed applications for same. This application is a continuation of U. S. application Serial No. 35957, filed June 23, 1915, and U. S. application Serial No. 214,849, filed February 1, 1918, so far'as concerns that portion of the disclosure which is common to them and the present application as to such matter as is common to the earlier applications.

Fig. 1 shows a cross section of a destroyer through the oil tank between the points 12 and 13, 12 being the port side, and 13' the starboard side, 24. being the deck forming the top of the oil tank, and 3 being the sea level. 16 is a submarine signaling device, preferably an oscillator of the type described in U. S. Patent 1,167,366, issued January 4, 191.6. 29 is an acoustic screen formed by streams of air bubbles issuing from the perforated pipe 30, the perforated p1pe occupying the position of the lower edge of the screen. If it is desired to have the oscillator 16 receive signals arriving from the port side, the air screen 29 is suppressed by closing the air supply to 30. When it is desired to screen the oscillator 16 from sounds arriving from the port side, air is admitted to 30, and a screen of bubbles is formed and produces the desired shield effect, 0., in effect a sound insulating wall in the liquid, the air bubbles being within one quarter wave length apart.

The screen of bubbles may be formed on the outside of the ship in the manner shown to the right of Fig. 1, and in Fig. 2.

Here 31, 31, 31, are curved segments formed on the outside of the ship and following approximately the stream lines of the ship as described in U. S. application 35957, filed June 23, 1915, for reducing the skin friction. 32 is a source of air under pressure, is a valve, 34 is a feed pipe for carrying compressed air to the feed pipes 35, 35, 35, 35, 35, which feed pipes carry the compressed air to the outside of the vessel, between the segments 31, 31, 31, 31, 31, thereby forming a screen of bubbles 36, as shown.

This screen of bubbles 36 may be used not only as a screen for the receipt and transmission of compressional waves by the oscillator 16, but may also be used to shield the ship itself from the effects of explosive waves such as would be produced by a terpedo or a depth bomb exploding in the water outside the ship, as described in the application of which this is a continuation, i. e., U. S application Serial #35957, filed June 23, 1915; and may also, as described in said Patented Aug. 3, 1920.

application, be used to diminish the skin l'riction resisting the passage of the ship through the water.

This type of sound. screen, as based on applicants discovery, has many advantages over the types previously used. It is very much lighter than the ordinary sound screen, and may be placed in situations where the ordinary sound screen would require elaborate fitting, and is extremely effieient. Another advantage is thatwith this type of sound screen if the air is shut off from both the pipe 30 and the pipe 34, the.

operator can hear sounds coming from all directions, and can send in all directions, and then, having detected a sound, can open the valves leading to the pipes 30, 34, and by noting which valve must, be opened in 'order to cut out the sound can determine the direction from which the sound is com ing.

What I claim is:

1. The'method of screening from the effects of compressional waves in liquids which consists in maintaining a stream of discontinuous air bubbles between the source of the waves and the object to be shielded.

2. Means for shielding objects from the effects oi compressional waves in fluids, said means consisting of a continuous stream of discontinuous air bubbles immersed in the lluid and located between the source of the waves and the object to be shielded.

3. Means for shielding objects from the ell'ccts oi compressional. waves in fluids, said means comprising a perforated pipe located in the fluid, and a source of compressed air,

whereby a stream of discontinuous air bubbles are formed and maintained in the fluid.

4:. That method oi. screening from the effects of compressionable Waves in liquids which consists in maintaining a stream of discontinuous air bubbles in thelliquid, the distance between adjacent air bubbles in the stream being less than one quarter wave length of the compressionable wave whose lengths are to be screened.

REGINALD FESSENDEN. 

